I’m going to a Burns’ Night party this year, my first ever; I have little or no Scottish blood in me (although I have been persuaded to don a kilt) and it will be my job to toast the lassies.
Any suggestions, anyone?
HAVE FUN!
My toast is “To the Cork and Bottle.”
And don’t worry, just a taste of haggis is all that is required - you don’t have to eat the whole thing.
Just remember - wearing underwear under your kilt is tantamount to a death wish, especially if you are found out!
A good toast for the softies is: “To friends: both here and gone. Those that could not join us tonight are held dear within our hearts. Let us drink to them.”
And as an addendum: “And let us drink until they feel it!” 
Well first of all, congratulations, it’ll be a lot of fun. Secondly, I promise that after one taste you’ll be only too happy to finish the haggis.
The “Toast to the Lassies” is exactly what it says it is - you can’t get away with being generic. You have to toast not just lassies in general but the actual specific lassies there on the night. I hosted a Burns’ Night Supper a couple of years ago (and I’m gutted that I’m away for it this year or I’d be hosting one again) and the guy I got to do it had a frankly brilliant formula for his toast. What he did was:
Start off by praising the attractiveness of all the attendant lassies - fair enough, as Burns had a legendarily keen eye for women. Then, and this was the good bit, he singled out each of the women there and explained why Burns would be only too delighted to make their acquaintance - for those he (the toaster) knew well, it was based on personality, well known stories about them etc., for those he didn’t it was based on e.g. jobs, hobbies, anything he could glean. He knew a bit about Burns’ life story and a few of the poems and referred to them to bolster his case, but it was hardly academic. E.g we had an accountant, so Burns’ time as an Exciseman got a mention; the two American girls occasioned a verse from his pro-Revolution poem, etc. The joy of this was that everybody felt included and when we rose to drink the toast we knew exactly what we were drinking to. It was also a good springboard for conversation/flirting later in the night.
Of course, this relies on their being only a handful of lassies to toast (we had four or five, from memory), and those one’s that you know or you can get good stories about - otherwise you’ll take too long going round them all and/or not have anything to say about some of them. In that case I’d suggest beefing up the generic stuff about attractiveness, joy to spend the evening with, looking forward to dancing, maybe something about why women are generally wonderful, and then singling out VIPs - anyone who’s been involved in organising the event, for example - for special attention.
You’ll know best how to pitch it for humour and tone; as ever keep it reasonably short and snappy (if you’re not going first, check audience reaction to the lenght of other toasts) and have fun with it - it’s all about making it a joyful occasion.
Also, be advised that after your toast to the lasses, the lasses get the chance to respond in kind.
Update:
I plan to conspire with the person responsible for the lasses’ response - simply because I’m going to depart from the hosts’ request that I (mildly) lampoon the failings of the lassies present (I simply can’t bring myself to do it.
I have been kitted out with an authentic kilt and regalia (including a dirk).
I’m really not looking forward to this.